mercruiser 150 HP I/O burning points

[djwalters]

I have recently purchased a pristene 1966 Starcraft with a 150HP Mercruiser I/O inline 6 cyl. Chevy. Within 15 to 30 minutes of run time it fries the points for some reason? I am using all Mercruiser parts. I've changed the points, plugs, condensor, rotor, and coil. Points and coil several times. Engine runs fine until it just stops because of lost fire through the points? Oddest thing, seems to happen most often when making a hard turn? Could it be my alternater putting out too much juice at periodic times causing some type of weird voltage spike? What about the resister wire the manual says it has? How do I know where it is and if it is OK? Can I replace the resister wire with standard wire and then use an automotive external resister, and automotive coil, to cut the voltage to the points back below 12 volts? ( I know I would need an additional wire from the starter solenoid + post for the initial start up voltage ). Boat is super nice, but I'm getting tired of paddling it back in. Hope someone out there can help me out of this mess. Thanks so much, Dave

 

[djwalters]

Re: mercruiser 150 HP I/O burning points

CORRECTION: I've replaced the points and CONDENSOR several times,the coil only twice.

 

[rattana]

Re: mercruiser 150 HP I/O burning points

What is the voltage between the positive side of the coil and the engine block when it is running? If is too high it will burn your points

 

[Dunaruna]

Re: mercruiser 150 HP I/O burning points

Most likely a faulty ballast resistor (or its been bypassed). Start with a DVM and check your voltages as rattana said.<br /><br />Aldo

 

[DJ]

Re: mercruiser 150 HP I/O burning points

Agree with the preceding.<br /><br />If you have 12 or more volts to the coil, you WILL fry points/condensers/coils.<br /><br />The voltage should be around 9.8 V.<br /><br />If more, you need a ballast resistor. Radio Shack can fix you up with the proper resistor to get your voltage within acceptable levels.<br /><br />By the way, don't think about turning that engine over about 4200 rpm's. It doesn't like it and you'll do nothing other than burn more fuel.<br /><br />Prop it to turn about 4300, with a LIGHT load.

 

[trog100]

Re: mercruiser 150 HP I/O burning points

cant see as having a faulty resistor wire.. or in other words a full 12 volts at the points would burn them out that quickly.. in fact i am sure it wouldnt.. we are only talking 2 volts or so difference here..<br /><br />course the problem is u seem to have changed every thing that could affect this.. and it only happens when u turn right.. ????<br /><br />No 1.. the condensor is there to stop premature points burning.. what happens is when the secondary circuit in your coil feeds a high voltage to the plug.. (points open) a back voltaqe of about 300 volts or so gets fed back to the points.. the condensor shorts this to earth.. if it isnt working your points wont last long..<br /><br />No 2.. the resistor to cut the power going thru the points and coils primary circuit.. well yes if it aint working your coil and points will not last as long as they should.. its possible the coil would die before the points.. but it aint gonna burn out points in 30 minutes..<br /><br />No 3.. faulty coil.. the primary coil circuit has less resistance than it should.. this is what really governs the current that goes both thru points and coil.. a sports coil will pass more current than a normal one for example..<br /><br />your point are simply a mechancial switch.. to burn em out that quickly would need one hell of a lot of current going thru em.. where is it going is the answer.. if its going thru the coil that is gonna be getting very hot.. check to see if yours is..<br /><br />i know u have replaced everything that matters just to make things harder.. he he.. i would get rid of your points and fit a transistorized ignition gizmo and coil that matches it to be honest.. i think they can be had for about $100 and are pretty easy to fit..<br /><br />trog100

 

[Don S]

Re: mercruiser 150 HP I/O burning points

cant see as having a faulty resistor wire.. or in other words a full 12 volts at the points would burn them out that quickly.. in fact i am sure it wouldnt.. we are only talking 2 volts or so difference here..

When the engine is running, he should only have between 8 and 9 volts going to the points. When the engine is running the alternator is putting out approximatly 14.3 Volts. That 6 volts difference, not 2. <br />You MUST have the resistor wire or ballast resistor installed or you will burn up points.<br />The wire from the starter solenoid puts full voltage to the points for easier starting, once the starter is off there is only the 8 or 9 volts to the points. And if the alternator is putting out too much voltage, you can burn up points very quickly. Also check that you don't have the coil wires hooked up backwards. The wire going to the distributor will be the negitive (-) side of the coil.<br /><br />Here is a diagram of a typical Mercruiser points system.<br />

 

[trog100]

Re: mercruiser 150 HP I/O burning points

there isnt 6 volts dfference don.. not at the coil there isnt.. u quote actual alternator output (no voltage drop) compared to what should be at the coil.. which is voltage drop over twenty feet of cable plus resistor wire.. the 13.5 average system voltage with the engine running does not get to the coil even without that resistor wire in circuit and twenty feet of cabling is probably a minimum i can imagine more in lots of cases <br /><br />after its gone all the way to the ignition switch and back its more like 12 volts engine running that that would get to the coil.. the resistor wire takes it down to about 9-ish.. i would say a difference of 3 volts max..<br /><br />plus i did not say u didnt need a resistor wire of course u do.. i simply said that on its own it would not cause points to burn out in thirty minutes.. i stick to that one..<br /><br />u say burn quickly but u dont say how quickly.. quickly could be a month.. it could be a week.. it could be a day.. do u think quickly could be 30 minutes.. i dont..<br /><br />burning up points isnt the most important issue here either.. its buring up coils.. they cost a little more than points..<br /><br />as for throwing in a defective alternator bunging out too much voltage.. well it certainly aint gonna help things now is it.. he he<br /><br />and the bypass wire to the coil dosnt put full voltage to the coil for easier starting.. what it actually puts to the coil is whatever is left after that super duper heavy drain starter motor has had its share.. this varies of course but in cold weather it could be as little as 7 or 8 volts getting to that coil..<br /><br />which of course is what using less than 12 volts coils is all about.. the ability to compensate a little for that big brute of a current draining voltage dropping device called a starter motor.. <br /><br />trog100

 

[Don S]

Re: mercruiser 150 HP I/O burning points

 

[rodbolt]

Re: mercruiser 150 HP I/O burning points

I feel your pain DonS

 

[rattana]

Re: mercruiser 150 HP I/O burning points

If the alternator is putting out 14.2VDC, it is very possible that there could be 14.2VDC at the positive side of the coil, especially if the ballast resistor or resistive wire has been bypassed by a rewire job by a previous owner. (1966) Who knows, maybe the regulator has gone t**s up and the alternator is putting out even more than 14.2VDC. A voltage check while it is running would ease the pain.

 

[Laddies]

Re: mercruiser 150 HP I/O burning points

I have had the bypass on the solinoid short out on two differant boats in the last two years causing pts to burn and in one case the coil to boil the oil out of it---Bob

 

[TwoBallScrewBall]

Re: mercruiser 150 HP I/O burning points

Trog, no offnese, but the points, and the coil can and will burn out that fast if they're seeing full charging voltage. They may last longer, they may not. <br /><br />You should be able to get a full voltage, maybe minus a couple tenths of a volt, out of 20 feet of wire or longer. <br /><br />

and the bypass wire to the coil dosnt put full voltage to the coil for easier starting.. what it actually puts to the coil is whatever is left after that super duper heavy drain starter motor has had its share.. this varies of course but in cold weather it could be as little as 7 or 8 volts getting to that coil..

No offense again but this is incorrect. The starter, when engaged, passes through the solenoid a full voltage to the coil and points to assist in starting. If your voltage dropped that low when you hit the key you likely wouldn't crank. After the starter disengages the bypass wire is de-energized and the coil should see the resistor wire voltage.<br /><br />DJw, First thing to check is the voltage at the coil as described above while the engine is running. Be careful and don't get zapped. If you see anything near 12-14 volts you need a new resistor wire. <br /><br />Also be sure to check and double check the gap and dwell when you reinstall new points. Incorrect gap will also burn them out quick.<br /><br />Hope this helps!

 

[djwalters]

Re: mercruiser 150 HP I/O burning points

Man, you guys have given me a lot of info to digest. Actually, trog100 may have the best solution by going to an electronic conversion. I will try one last time in the spring with the various suggestions above, with the comfort of knowing I can always switch to the breakerless system. Thanks so much for all of your help, Dave

 

[FreeBeeTony]

Re: mercruiser 150 HP I/O burning points

I would install the Petronix conversion kit.........and eliminate the resistor wire.<br />I did it on my 165 IL6.

 

[Bt Doctur]

Re: mercruiser 150 HP I/O burning points

Burned up a few sets with 2 or 3 runs at the strip.you need the voltage reading at the + side of the coil with the motor running to get a handel on what is going wrong.Arcing burns up points,the condensor controls this within the voltage limits.more than 7-9V will eat them up in no time at all.IF the res. wire was by-passed try a "internal resistor coil" and make sure the coil polarity is correct. + side goes to the 12V wire.Even if you go to electronic ,if the voltage is out of line youll fry them too.

 

[DJ]

Re: mercruiser 150 HP I/O burning points

There you go. Take FreeBee's advice.<br /><br />BTW, Don S and Bondo's advice were dead on.<br /><br />Still, the Petronix may require a resistance. Check it out.

 

[trog100]

Re: mercruiser 150 HP I/O burning points

for what its worth my points type resistor wired boat reads 10 volts at the coil input side.. 12.5 at the choke positive connection which is the same piece of cabling that feeds the resistor wire except it goes straight off to the choke.. the gauge on the dash reads 14 volts..<br /><br />the resistor wire seems to cause a voltage drop of 2.5 volts.. the cable run a voltage drop of 1.5 volts.. not quite what folks say things "should" be but the points dont burn any quicker than they should.. the coil dosnt get hot.. and things work okay..<br /><br />i quote an actual working example.. not manual figures or theory..<br /><br />and yes my voltmeter is accurate but i doubt the one on the dash is thow..<br /><br />as for what voltage is left in the system while the engine is being cranked over with the thickish mercruiser oil in the sump on a cold winters day.. dunno i aint checked that.. but i doubt its anywhere near 12.. still its a problem summer only boaters dont have to worry about.. <br /><br />the petronix ignition kit seems the one to go for especially the more expensive one on offer..<br /><br />i also feel the pain.. u bible quoting guys really would have me worried if it wasnt for the fact i have gone thru sixty years of life involving much "mechanicking" without too many problems.. he he<br /><br />my current problem is how to get a twenty foot plastic boat sat on sandbags out of someones garage and on to my trailer.. thats one for tonight.. anybody have a manual on how to do that.. ???<br /><br />trog100

 

[TwoBallScrewBall]

Re: mercruiser 150 HP I/O burning points

I second the recommendation for electronic ignition. I got stranded by the points/coil ignition on my boat, towed in by the coust guard.<br /><br />I found a nice gentleman here with a Delco EST he wasn't going to use. Night and day difference. Idled much smoother, setting the timing was easier and you could really see the advantage there. Where the timing mark would bounce around a couple degrees with the points, it was rock solid with the electronic ignition. <br /><br />I agree with ya Trog, experience is what really counts. Again I never meant to offend you or anyone, I sometimes hesitate to post sometimes just because I don't want to deal with the flaming afterward. I am in fact a summer boater, and judging by how slow my 11 month old truck cranked over this morning at -4F you're proably right about the drastic drop at those temps. <br /><br />Good luck!

 

[djwalters]

Re: mercruiser 150 HP I/O burning points

I just want to say thanks to all of you guys. With all of the information you sent, I'm sure I will be able to correct the problem once the weather breaks, Dave